Concept 3 AP BIO

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH . The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C . The results of the experiment are represented in Figure 1.

Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment ( pH near 6) to a basic environment will have on peroxidase activity?

• Peroxidase activity will decrease.

• Peroxidase activity will increase.

• Peroxidase activity will stay the same.

• Peroxidase activity will increase at first and then decrease.

Aminolevulinate dehydratase ( ALAD ) is an enzyme that relies on zinc as a coenzyme. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD .

Which of the following statements best helps explain how the lead ion causes inhibition of ALAD ?

I

• It changes the shape and charge of the substrate so that it becomes more compatible with ALAD ’s active site.

• It changes the amino acid sequence of the ALAD protein so that the enzyme catalyzes a different reaction.

• It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate.

• It changes the enzyme-substrate complex so that the transition state is more stable and the reaction proceeds at a faster rate.

Tags

NGSS.HS-PS1-2

A researcher proposes a model to explain how enzyme-substrate interactions determine enzyme specificity. The model is based on the idea that substrate molecules form favorable interactions with the amino acid side chains in an enzyme’s active site.

Based on the model, which of the following statements best explains an enzyme’s specificity for a particular substrate molecule?

• A hydrophilic molecule interacts with nonpolar side chains in the enzyme’s active site.

• A hydrophobic molecule interacts with polar side chains in the enzyme’s active site.

• A molecule with positive charges interacts with positively charged side chains in the enzyme’s active site.

• A molecule with negative charges interacts with positively charged side chains in the enzyme’s active site.

Researchers investigated the effect of urea on the three-dimensional structure of a certain enzyme. The researchers dissolved the enzyme in an aqueous buffer solution and added urea to the solution. The enzyme did not appear to have a secondary or tertiary structure. The researchers carefully removed the urea from the solution and determined that the enzyme had the original secondary and tertiary structure again.

Based on the results of the experiment, which of the following statements best predicts the effect of urea on the enzyme’s function?

• Function will be disrupted by adding the urea and regained by removing the urea.

• Function will be disrupted by adding the urea, but it will not be regained by removing the urea.

• Function will be gained by adding the urea and disrupted by removing the urea.

• Function will be unaffected by the addition and removal of the urea.

A researcher claims that spinach leaves capture the most energy from light waves in the range of 500 nm to 600 nm . To test the claim, the researcher will place spinach leaves in separate chambers and expose the leaves to different wavelengths of light. For each chamber, the researcher will measure the amount of oxygen gas (O2) that is produced in one hour.

Which of the following graphs best represents data from the experiment that will support the researcher’s claim?

• 
• 
• 
• 

Tags

NGSS.HS-LS1-5

A researcher claims that the initial rise of oxygen in Earth’s early atmosphere, which occurred approximately 2.3 billion years ago, resulted from the metabolic activity of prokaryotic organisms. The claim is based on an interpretation of the geochemical and fossil evidence represented in Figure 1.

Which of the following types of evidence will best support the researcher’s claim?

• Evidence that some of the earliest eukaryotes used oxygen to produce ATP by cellular respiration

• Evidence that the earliest plants produced oxygen as a by-product of photosynthesis

• Evidence that some of the earliest organisms carried out photosynthesis without producing oxygen

• Evidence that the cyanobacteria produced oxygen as a by-product of photosynthesis

A researcher claims that a certain herbicide suppresses plant growth by inhibiting chloroplast function. To test the claim, the researcher treats isolated chloroplasts with increasing concentrations of the herbicide. The data from the experiment are presented in Table 1.

Which of the following statements best clarifies how the data support the researcher’s claim?

• The thylakoid membrane is more permeable to carbon dioxide than to polar molecules.

• ATP synthase activity depends on a proton gradient across the thylakoid membrane.

• Some enzymes embedded in the thylakoid membrane catalyze the hydrolysis of ATP .

• Carbon fixation in the Calvin-Benson cycle takes place in the stroma of chloroplasts.

Tags

NGSS.HS-LS1-5

NGSS.HS-LS2-5

Phycobiliproteins are a complex of accessory pigments and proteins found in cyanobacteria but not in green algae. A researcher claims that the phycobiliprotein pigments in cyanobacteria allow the cyanobacteria to survive in certain aquatic niches better than green algae can.

Which of the following statements best justifies the researcher’s claim?

• The additional pigments allow the cyanobacteria to store light energy so that it can be used at night to continue photosynthesis.

• The additional pigments block light and prevent it from reaching photosynthetic organisms at greater depths, so no photosynthetic organisms can live below the surface waters containing cyanobacteria.

• The additional pigments require energy and cellular resources to produce, so they can be used as an energy source during times of insufficient light.

• The additional pigments absorb light at wavelengths that green algae cannot absorb; this may allow cyanobacteria to capture more light energy for photosynthesis than green algae can in certain areas.

During respiration, most ATP is formed as a direct result of the net movement of

• potassium against a concentration gradient

• protons down a concentration gradient

• sodium ions into the cell

• electrons against a concentration gradient

Tags

NGSS.HS-LS1-7

To investigate bacterial metabolism, a researcher divided a population (culture) of Staphylococcus capitis bacteria into two sets of culture tubes containing glucose. The researcher added a chemical to one set of tubes and measured the pH of the cultures at 5 -minute intervals as the bacteria metabolized the glucose into lactic acid. The data are shown in Table 1.

Which of the following was the dependent variable in the researcher’s experiment?

• Time

• pH

• Glucose concentration

• Lactic acid concentration